Semiconductor signal translating device



July 15, 1952 R. J. KIRCHER sEMrcoNnucToR SIGNAL TRANSLATING DEVICE 2SHEETS-SHEET 1 Filed May 5, 1951 FERMI LEVEL A 7' TORNEY July 15, 1952R. J. KIRCHER SEMICONDUCTOR SIGNAL TRANSLATING DEVICE 2 SHEETS-SHEET 2Filed May 5, 1951 -32 48 COLLECTOR BIAS VOL TS /6 -32 COLLECTOR BIAS VOLTS /NVE/vro/P v R.' J. KIRCHE/P A TTORNEY Patented July 15, 1952 UNITEDSTATES PATENT ori-ica sEMIcoNDUcToR SIGNAL .'rRANSLATING'y A f f DEVICEReymond J. Kircher, Summit, N. J., assignor to 'Bell TelephoneLaboratories,- Incorporated, i

New'York,'N. Y., a corporation of'New` )fork- Application May 1951,seiial'o. 224,777 v "u This invention relates to semiconductor signaltranslating devices and more particularly to such devices of the typedisclosedY in Patent 2,524,035,

granted `October 3, .1950, to J. Bardeenl and W. H. A

Brattain.

Devices of the type :ldisc-:losed` in the patentV above identified,which are known as transistors, comprise, v.in `general, a bodyofsemiconductive.

material having a large area or substantially ohmic connection,` termedthe. base, thereto :and having also associated therewith two otherconnections deisgnated the emitter andzcollector. Inf-one manner ofoperation, signals aref applied between the emitter and base andreplicasthere-v of "are robtained ina loadlcircuit connected be.

tween the collector and base. Y Y

Thev mechanism of vtranslation involves the injection, at the emitterand into the semiconduc'tive body, of charge carriers of sign oppositethat of the vcarriers normally in excess vin the bulkfofthesemiconductive material. Specicalv ly,-of the body is ofAN`conductivity-type,'for

example -Ntype germanium, the" carriers nor-v mally in execess-fthereinarenelectrons -and Ythe injected-'carriers arerholes; if the body isvof-y P conductivity-type, thec'arriers vnormally* in `excess thereinare holesan'd the injected carriers are'electrons. vr*The collector isbiased at the polarity to attract the injected ca'rriersthereto.VThusffor example, -for the case of an N conductivi'ty-type body, thecollector'is biased negative which is markedly dependent upon both theemit-V ter current andthe potential of thel collector.-

Such-variations or noiset components. tend -to obscure` thetranslationof signals.

- Onelgeneral object of; this invention is to im-v prove: theperformance characteristics. of -semi-Y conductor/'signal translating.devices. `More speclcally, objects of this.` invention are to improve'the vfidelity. of translation of signals by such .de-` vices,to.reducenoise inthe output of transistors 16 Claims.v (Cl. 175-366) Inaccordance withne feature of this'finven-i'- tion, lin semiconductortranslating, devices-poi f the-type describ'ed'hereinabove, a barrieris'provided within th'ebfd'y :to substantiallyimpede' the ow tothecollector region of'carriers ex-l traneously generated within thebody- 1Yin accordancewith lafmbrel specific feature of u this invention',`there is 'provided "withinA 'the body and in proximityltothecollector azone 4or regionv of the same conductivity-typefas the body butv ofsubstantially vhigher conductivity'than the bullov ofthebOSYf.. f v 'i``In o ne illustrative embodiment of thisr inventionja transistor`comprises* a body of' N 'cone ductivity-type germanium' having thereinavery' narrow regonir-acne,y which may be a 'grain'.v boundary,` also ofN-type'but of substantially greater conductivityxthan the bulk. of the.body.

andftoobtain a, .uniform signal to noise Jratio.

overfafvvide range ofcollector potentials.

VNoise in a transistor mayV lie-ascribed, in partA atleast, to the.random or 'sporadic generation withingthe semiconductive body ofcarriersLof like` sign to those injected, at the emitter, and the flowerthesegenerated carriers tothefcol-` lectorregion. Y y 'i Y i' baseandemitter connections vtov the body, and a collectorconnection on thehigher conductivity region or grain boundary. The collector oonnectionmay be, Vfor example, aj point contact' bearing ,againsty the boundaryregion or zone.

In another illustrative embodiment of this invention,y a,transistor/*comprises a vbody r`of N conductivityftype germanium havingIon one face thereof a thin layerofNv-type germanium of ,con-s ductivitysubstantiallygreater than that Vof .the body bulk material, a=base'iconnection Vto the body, and-emitter and collector, connections,to.4 the face layer... 11, Y, The .invention and the above notedandpther. featuresthereof willbe'understood more clearly andzfully from"the followingidetailed'description with referencer to thel accompanyingdrawing inI Fig. l isza, diagram illustrating';the principal; componentsand the.associationtherof,ina sig-,- nal translating. deviceillustrative of one em. bodiment of this invention;v y f Fig. 2 .is anenergy-.level diagram-forthe semi` conductive bodyv .included betweenr:Ythe emitter and collector connections inlthe `device shownin- Fig. A3Yis al -plan view of vthe translating device of Fig. 1showingftheposition'of the emitterand which. the points are placed' 5 is'an-energy ,diagrami represents-'g collector with respectftojtheNffregion-*in the;

. and;engagin'g -boththe; Nzonesxandgalso 1th,@ y zone. Bearing againstthe opposite face of; the;Y w body.-f 2-are:.an emitterfZSI-andcollector 21,6both i ofgwhichgmay .be point Vc ontactsfor l example thecollectonpf.phosphor -bronzeand the emit beryllium'fcopper. Theemittrfpointabe i y the..-N,region, l,the Vcollector,point on the Yductor bodyin the device shown in Fig". 4, taken across'the NrN+interface; Y

Figs. 6 and 7 kare elevational views of other illustrative embodimentsof this invention;

Figs. 8 and 9 areV plan and elevational views `respectively of aiilamentary type transistor illusn Y trative ofj'still anotherembodiment of thein# vention; and

Figs. 10 and 11 are graphs depicting perform-J.

ance characteristics of typical point contact tran--VV sistorsconstructed in accordance. ffwith. .this y;

invention.

In the drawing, in the interestofclarity,cere tain dimensions have beengreatlyexaggerated;i' Vthen-magnitude ofthe exaggeration KY,will be;appar-4 ent from the typical dimensions given hereinafter.

` AISO in the drawing, in the -semiconuuctiv bodies the portions orregions of relatively low conductivity haveibe'en designatedN+:^ There-v t sistivity.` ofth'e Nimaterial may befor'jexarnplejoflthefordeibfl'.ohm centimeters and-resistivity of..v the.. N t'material? may bejof "the" order of* 'Y ohm centimeters.'

position. A heat-zp robe'giv-ingV 'a *galvanometer deflection dependingon the N concentration may alsoj'be--used-s-'l Suitable .germaniumAmaterialginV` cluding'N and N+ regions orzones,which inthiscase Vare.not crystal f-gra'in boundariesvf-may be produced a-lsoin themannendisclosedlin the =ap l ReferringJ now-to vlthe. drawing.: thesignalltranse.

latine-#deviceillustrated in `Fi'gffl comprises-'a fconductivity havebeen indicated by the letter N andthe. portions orregions .of relativelyhigh L 2'! and signals to be translated are impressed upon theemitter-base circuit from a signal source 28; A suitable resistor 29 maybe connected in the emitter-base circuit as shown. The collector 23 isbiased at a relatively high potential in the reverse direction relativeto the base 24 by a'source 30 A load represented A generally by theVresistor 3|"is connected" inthe` collector toA base circuit as shown.Amplified replicas of the signals impressed by the source 28 areobtained In the illustrative embodiment of this invention illustrated inFig. 4, the semiconductive body `2700Vincludes-an N-type portion 2| Dhavingon fl one surface thereof an N+ layer 32 which may beforexampleiof the order of,0,.004 inch thick. The base .connection V24 ismade to the N zone ZIO and the emitter and collector 25 and 2G `whichvmay bein the form of Vmetallic point contacts,

bear against the N+ layer32, the spacing betweenthe emitter-fandcollector being vapprox-ivmately0.00K2finch. L f y f In anotherembodiment; of. this. inventions111-.;`

lustrated in Fig.` .-6. the .semiconductivebody of the same constructionas that in theadevicei.l

illustratedinsl'ig'.` .14, 'rbut the: emitter 25.3bears against the. N.zone ;or rportion; 210 .andi the icolif; lectorz2 'bears against`thegN-tV ,zone532 atfazpointa junction-,1 .i between the N andffN+fregions..orzonessc in immediate proximity tothe barrier. vor

that.. showninf Fig. ,4 but` vincludes-fan'.l .additional contact 3.3,'*forrexample in;the form; oiga @pointer edwire, bearing lagainstrtheinterface orrjunction .l, between 'the' N zoney2'l0and the- N+;la.ye`r.32.Y InJ a similar way an additional pointrmaysbe useds on theinterface of the twor regionsfof VFig.;6 on the;,;Ntfregion.f Y Y j i-Theinvention may be ern-bodied also-inqfil mentary; rtype transistorssuchj-,asadisclosed an Patentl 2,502,479.- granted'fApril-4;.1;950.,:.t0i-G-=i .f Pearson 4and fW-.g- ,Shockley 'f In one.fconstruction illustrated-in ,Figs.8 and9, the vsemicond-uctiveTsemiconductorbodyz2; for: exampleof .ger-f y 1 manium, having thereintwo N zonesJ2I rand .22:1V

bodyi.2 0, @this :connectionf :constituting:y thefbase gian cran theedgejthereofgTngzemittertgoif lector; spacing "advantagfeQI'ASIyjisvsubstantially o .o'ozzimn'Y the emitter V25 is biased-"iat a low-vo1ta`-ge l inthe' n g for'WardicurecmmV reianve-ftfthebody by a.' scezone'23 dened forrex'amplefby a. suitablefcryse; e YtalL:boundaryextendingthroughthersemiconducg: tive'afbo'dy: Infonelillustrative construction therA y body may be a wafer .075 inch long,.075 inchffwidef 1 andx20finchthick andztheiNtzone orboundary maybefs'ubstantiallyzOOO:inch thick-' '.i, i

i VA large areaor.v substantially. ohmic connection; e 24, which may be,for:;example,..a coatingitofr' toL ' pere.. It :will be snotedffro'm1Fig" currentwmultiplication vfacizorefza 1sisubst'aritiallitIforifafbandwidth of ne'lcycl'erf 35 connected by an intermediatefilamentaryporf;

tion. Thebody includes an N zone .orregionl-and.

a thin N+ layer/.V32 extendingover Aa parte of the,

N vzone or fregion. f The :base `connecftiongfi..40fis a metallic`coating o'nnzrtloev enlarged; endvpart metallic coating uponthe.enlargedNrportion.. 25.'

butgconnectedfto vthe Ntlayer. :'Ther emitter.Performa-ncef@harastatistics f :devices 'icon-1. structedr inaccordance; withthis::in ventioi-iyare.,V portrayed ;in;Figs.jyi10.zandr141 :YSpeiciiically;:theY characteristics presentedrin FigszflOAf.andalOB are for a Y transistorsofnthe 'constructiontvshowm in Fig. 1 and,described hereinabovfiwith;the

' collectorg26xbearing against,.or lrimrnediatelmad#` for .aconstantemittencurrent' ofgtLDzmilliam-e.

constant over awide frange', of collectorwoltagesr The :baseband emitterresistances alsa'vwere: suba: stantially constantover:,thisrangerthebasetutee sistanc .beingrabout L50.; ohrnsand the!"4emitter resistancefbei'ng Aabout flgvto'hms. cfIhe kno'iseeislgf;

collector noise figure considered vsep"afrately'Care substantiallyconstant overl this collector voltage f Theimprovement realized by thisinventionfinl the collector-noise figure oftransitors is indicatedclearly in Figs. 11A.and 11B. In the former, line A shows v'theV.averagecollector noise-collector withI the-collectorfZG uponorimmediately adjacent the N+N+ boundary, and in Fig. 4. -Sin-1i-27|larlyinffFig.y 11B', curves Ajand B, depict the emitterjnoise-collectorpotential relation for prior art transistors andV transisitors of theconstructions *illustrated* in Figs. 1' and 4.1y Itwill notedfrom'HFigs. 11A andv 11B that in devices constructed in accordance withthisvinvention an improvement of the orderof l0 decibels is exhibitedfor both the emitter andl collector noise figures over a wide rangeofcollector potentials.

As has been noted' hereinabove; lin transistors, collector noise isascribable in part at least to the extraneous generation of holes in thesemiconductor body and flow of these holes to the collector region.Analysis of the energy level diagrams for devices constructed inaccordance with this invention affords an explanation for theimprovement in noise figures realized in such devices. In Fig. 5, whichportrays the energy levels in a device of the construction shown in Fig.4 and described hereinabove, line C represents the bottom of theconduction band and line F the top of the filled band for the N and N+zones or regions, the Fermi level being as indicated. It will be notedthat at the interface between or junction of the zones or regions, theenergy level contours are such as to impose a barrier to the readypassage of holes from the N into the N+ region. Thus, by virtue of thesemiconductive body structure the collector is shielded from the holesgenerated extraneously in the bulk of the N region whereby collectornoise is reduced.

Similarly, as will be seen from Fig. 2, which portrays the energy levelsin the semiconductor body of devices of the construction shown in Fig.l, because of the N+ region a barrier is presented to the flow of holesgenerated in the N region 22 from this region to the vicinity of thecollector, whereby a reduction in collector noise is effected.

The magnitude of the barrier to such flow of holes may be controlled,for example increased, by application of a potential to the N+ region asby Way of the auxiliary connection 33 as illustrated in Fig. '1.

Although in the specific embodiments shown and described thesemiconductor body is of N conductivity-type, the invention may bepracticed also in devices utilizing P-type bodies, the higherconductivity zone in this case providing a barrier to the flow to thecollector vof electrons generated sporadically in the bulk of the body.

Also although in the speciiic embodiments shown and described a sharpchange in conductivity between zones has been set forth, noiseimprovements realized in accordance with this invention may be achievedalso by tapered or gradual changes in the bodyconductivity, from zone tozone.

Further, it will be understood that the several embodiments of theinvention shown and described are but illustrative and that variousmodifications may be made therein without departing from lthe scopeandspiritoff'this invenltion;

yWhatis claimed is:A

l. A' signal translating deviceconiprising ai) body orsemiconductivematerial of one conduc.

tivity-type, emitter, collector andlb'ase connections to said body, andmeans defining a barrier to the -ilow of charge carriers of signopposite" that of those normally present in salda-body, generated in=said body, toward said collector,said means comprising contiguous zonesof said-maj-l Y teriL-f'of like leonductivlij,y'type but of substan"tially different conductivity.

2. A signalA translating device comprising a#Y body of semiconductivematerial, andfemitter, i collector and baseV connections to said body,said body being-of one conductivity-type and-having therein in immediateproximity to said collector a zone of said type and of substantiallygreater tivity-type and having therein a region of said type but ofgreater conductivity than the bulk of said body, emitter andbase'connections to said body, and a collector connection to saidregion.

4. A signal translating device comprising a body of N conductivity-typegermanium having therein a zone of said type but of .greaterconductivity than the bulk of said body, emitter and base connections tosaid body, and a collector connection to said zone.

5. A signal translating device comprising a body of semiconductivematerial of one conductivity-type and having therein a zone of said typebut of substantially different conductivity than the bulk of said body,base and collector connections to said zone, and an emitter connectionto said body at a point spaced from said zone. Y

6. A signal translating device comprising a body of semiconductivematerial of one conductivity-type and having therein a region of saidtype but of substantially greater conductivity than the remainder ofsaid body, a point contact emitter bearing against said body at a pointspaced from said region, a point contact collector bearing against saidregion, and a substantially ohmic connection to said region.

7. A lsignal translating device in accordance with claim 6 werein saidbody is of N conductivity-type germanium. l

8. A signal translating device in accordance with claim 6 wherein saidbody is of silicon.

9. A signal translating device comprising a body of semiconductivematerial of one conducthe bulk of said body, a base connection to one ofsaid faces and contacting said region, and emitter and collectorconnections to the other of said faces, said collector connectioncontacting said region and said emitter connection being spaced fromsaid region.

10. A signal translating device in accordance with claim 9 wherein saidbody is of N-type germanium.

1l. A signal translating device comprising a body of semiconductivematerial having on one face thereof a layer of the same conductivitytypeas saidbody but of greater conductivity than the bulk of said body. abase connection to said body, and emitter and collector connections tolsaid layer.

conductivity than the remainderof said body.` 35A-'signal translating'device comprising a-' body of semiconductive material of one conduc-ff'

